Multiple dielectric filters are proposed, which each have multiple resonators on a dielectric substrate and which achieve desired filter characteristics by using the coupling between the resonators.
FIG. 1 illustrates a configuration of a dielectric filter disclosed in Patent Document 1. The dielectric filter 101 is a three-stage filter using three resonators. The three resonators are composed of lines 102, 103A, and 103B, respectively, provided on the same main surface of a dielectric substrate. The line 102 has a curved U shape and both ends of the line 102 are opened. The lines 103A and 103B each have an I shape. One end of the line 103A is connected to a ground electrode 105 and the other end thereof is opened. One end of the line 103B is connected to the ground electrode 105 and the other end thereof is opened. An input-output transmission line 104A is connected to the line 103A and an input-output transmission line 104B is connected to the line 103B.
In the above configuration, the filter characteristics, particularly, the passband depends on the degree of coupling between adjacent resonators. Accordingly, the dielectric filter disclosed in the Patent Document 1 shifts the positions where the lines are arranged to adjust the opposing lengths of adjacent lines in order to set the degree of coupling.
Patent Document 2 discloses a method of manufacturing a chip device comprising a surface-mount antenna. In the manufacturing method disclosed in this document, after a circuit pattern is provided on a dielectric host substrate, chip device elements are cut out from the dielectric host substrate and electrodes are arranged on side surfaces of the chip device elements to manufacture the chip device.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-358501
Patent Document 2: Japanese Unexamined Patent Application Publication No. 10-107537
In the dielectric filter described in Patent Document 1, the passband can be set by adjusting the opposing lengths of adjacent lines. However, it is not possible to finely set an attenuation pole toward lower frequencies of the passband in such a dielectric filter. For example, it is difficult to realize an attenuation curve that falls sharply toward lower frequencies of the passband.
In addition, since the degree of coupling is adjusted by shifting the positions where adjacent resonant lines are arranged, it is necessary to increase the amount of shift in the arrangement position depending on the degree of coupling that is set and the area of the circuit is consequently increased. Accordingly, with the configuration of the dielectric filter disclosed in Patent Document 1, the restriction on the area of the substrate of the chip device may not be met even if a desired passband is achieved.